A study of food chains in seagrass communities II. Food of the rock flathead, Platycephalus laevigatus Cuvier, a major predator in a Posidonia australis seagrass bed

Abstract

Feeding habits of P. laevigatus were investigated between February 1980 and November 1981 as part of a larger study on the structure of food chains supporting commercial fishes in the seagrass beds of Corner Inlet, south-eastern Australia. The main food components were crabs, predominantly Nectocarcinus integrifons, and juvenile fishes. Most dietary items were inhabitants of the seagrass zone. Small (25-33 cm) rock flathead showed a preference for fish, squid and shrimp whereas larger (> 33 cm) individuals consumed mainly N. integrifons together with some fish. Seasonal variations in diet and feeding intensity occurred. A decrease in feeding intensity in winter was accompanied by a shift in diet from N. integrifons to fish and squid. A second decline in feeding intensity corresponded to the apparent spawning period. The rock flathead and its main prey, N. integrifons, both showed a rhythm in locomotory activity correlated with nocturnal or crepuscular high tides whereas small fish prey were mostly active during daylight.